1. Field of the Invention
The present invention relates generally to a picture signal converting apparatus in which digital picture signals are converted, a picture signal converting method used in the picture signal converting apparatus and a picture providing system for providing picture signals obtained by converting digital picture signals in the picture signal converting apparatus, and more particularly to digital picture converting method and apparatus for directly converting digital picture signals based on a color component type or a compression format into digital picture signals based on another color component type or another compression format.
2. Description of the Related Art
Recently, a picture apparatus for processing digital picture signals has been often used, and digital picture signals of a color component type has been frequently used as the digital picture signals. In the digital picture signals of a color component type, a digital picture signal corresponding to one pixel is divided into a luminance signal Y and a first color difference signal Cr and a second color difference signal Cb, and there are many color component types respectively corresponding to a sampling frequency ratio of a group of two color difference signals Cr and Cb to a group of luminance signals.
A first color component type is a 4:4:4 color component type. As shown in FIG. 1A, one color difference signal Cr of one pixel and one color difference signal Cb of one pixel respectively correspond to a luminance signal Y of the same pixel for each pixel. Therefore, one luminance signal Y and two color difference signals Cr and Cb exist for each pixel. In this case, as shown in FIG. 1B, in cases where an X-Y co-ordinate system is considered for each type of signal Y, Cr and Cb, one luminance signal Y.sub.(x,y) placed at co-ordinates (x,y) corresponds to a pixel placed at co-ordinates (x,y) of a frame, two color difference signals Cr.sub.(x,y) and Cb.sub.(x,y) placed at co-ordinates (x,y) respectively correspond to the luminance signal Y.sub.(x,y). In this case, an information volume of luminance signals Y for one frame is the same as that of color difference signals Cr for one frame and that of color difference signals Cb for one frame. Here, x=0,1,2,3 - - - and y=0,1,2,3 - - - are satisfied.
A second color component type is a 4:2:2 color component type. As shown in FIG. 2A, one color difference signal Cr of one pixel and one color difference signal Cb of one pixel respectively correspond to two luminance signals of two pixels arranged in series. Therefore, as shown in FIG. 2B, in cases where an X-Y co-ordinate system is considered for each type of signal Y, Cr and Cb, one luminance signal Y.sub.(x,y) placed at co-ordinates (x,y) corresponds to a pixel placed at co-ordinates (x,y) of a frame, two color difference signals Cr.sub.(x,y) and Cb.sub.(x,y) respectively correspond to one luminance signal Y.sub.(2x,y) and one luminance signal Y.sub.(2x+1,y). In this case, an information volume of color difference signals Cr for one frame and an information volume of color difference signals Cb for one frame are respectively half that of luminance signals Y for one frame.
A third color component type is a 4:2:0 color component type. As shown in FIG. 3A, a color difference signal Cr of one pixel and a color difference signal Cb of one pixel respectively correspond to four luminance signals of four pixels arranged in a matrix of two lines and two rows. Therefore, as shown in FIG. 3B, in cases where an X-Y co-ordinate system is considered for each type of signal Y, Cr and Cb, one luminance signal Y.sub.(x,y) placed at co-ordinates (x,y) corresponds to a pixel placed at co-ordinates (x,y) of a frame, two color difference signals Cr.sub.(x,y) and Cb.sub.(x,y) respectively correspond to one luminance signal Y.sub.(2x,2y), one luminance signal Y.sub.(2x+1,2y), one luminance signal Y.sub.(2x,2y+1) and one luminance signal Y.sub.(2x+1,2y+1). In this case, an information volume of color difference signals Cr for one frame and an information volume of color difference signals Cb for one frame are respectively a quarter of that of luminance signals Y for one frame.
A fourth color component type is a 4:1:1 color component type. As shown in FIG. 4A, a color difference signal Cr of one pixel and a color difference signal Cb of one pixel respectively correspond to four luminance signals of four pixels arranged in series. Therefore, as shown in FIG. 4B, in cases where an X-Y co-ordinate system is considered for each type of signal Y, Cr and Cb, one luminance signal Y.sub.(x,y) placed at co-ordinates (x,y) corresponds to a pixel placed at co-ordinates (x,y) of a frame, two color difference signals Cr.sub.(x,y) and Cb.sub.(x,y) respectively correspond to one luminance signal Y.sub.(4x,y), one luminance signal Y.sub.(4x+1,y), one luminance signal Y.sub.(4x+2,y) and one luminance signal Y(.sub.4x+3,y). In this case, an information volume of color difference signals Cr for one frame and an information volume of color difference signals Cb for one frame are respectively a quarter of that of luminance signals Y for one frame.
2.1. Previously Proposed Art
A digital picture signal has been recently used in various video apparatuses such as a camera with a video tape recorder for public use or in the personal computers, so that a digital picture signal converting apparatus has been rapidly widespread. In general, the digital picture signal used in the personal computers and the video apparatuses for public use is compressed at a standardized compression format, and two types of compression formats are frequently used.
A first type of compression format is based on image compression standards of moving picture experts group 1 (MPEG1) or image compression standards of moving picture experts group 2 (MPEG2). The compression format based on MPEG1 or MPEG2 is often used for the picture signal used in a computer. In the compression formats based on MPEG1 and MPEG2, a time-redundancy between frames is reduced by performing a motion compensation, a space-redundancy in each frame is reduced by performing a discrete cosine transform, and a code volume is reduced by performing a variable length coding. MPEG1 is explained in a literature of ISO/IEC 11172-2 "Information Technology--Coding of Moving Pictures and Associated Audio for Digital Storage Media at up to about 1.5 Mbits/s--Part 2: Video", and MPEG2 is explained in a literature of ISO/IEC 13818-2 "Information Technology--Generic Coding of Moving Pictures and Associated Audio Information--Part 2: Video". Therefore, a detail description of MPEG1 and MPEG2 is omitted.
FIG. 5 is a block diagram of a conventional MPEG data producing apparatus in which MPEG data is produced according to the compression format based on MPEG1 or MPEG2.
As shown in FIG. 5, when a user uses an analog video apparatus 101 with an analog signal output terminal such as a video tape player or a video camera on condition that the analog video apparatus 101 has no digital signal output terminal, an analog picture signal output from the analog video apparatus 101 is converted into a non-compressed digital picture signal in an analog-to-digital converter 102. Also, when the user uses a digital video apparatus 103 with a digital signal output terminal, a non-compressed digital picture signal is directly output from the digital video apparatus 103. Thereafter, the non-compressed digital picture signal is input to an MPEG encoder 104, and MPEG data are produced from the non-compressed digital picture signal in the MPEG encoder 104 according to the compression format based on MPEG1 or MPEG2.
In this case, the non-compressed digital picture signal input to the MPEG encoder 104 is classified into the 4:2:2 color component type or the 4:4:4 color component type, all MPEG data based on MPEG1 is classified into the 4:2:0 color component type, and many MPEG data based on MPEG2 is classified into the 4:2:0 color component type.
A second type of compression format is based on image compression standards of DV, DVC, DVCPR0 or DVcam. The image compression standards are applied for a picture (or video) signal used in a digital video apparatus including a video apparatus for public use. Because signal data structures and compression formats based on DV, DVC, DVCPR0 and DVcam are similar to each other, DVC, DVCPR0 and DVcam are treated as DV in this specification. DV is image compression standards enacted in 1996 for a video cassette recorder and is based on "Specifications of Consumer-Use Digital VCRs (HD Digital VCR Conference, 1996)". A video apparatus using a picture signal based on DV has been recently widespread rapidly. Also, a video camera for public use has been widespread rapidly as a video apparatus using a picture signal based on DV, so that people can easily produce a picture signal based on DV at a low cost.
In the compression format based on DV, redundancy in each frame is reduced by performing a discrete cosine transform, and a code volume is reduced by performing a variable length coding. In addition, positions of data are changed in each frame in macroblock unit by performing a shuffling processing for a compressed signal based on DV.
A picture signal input or output to/from a video apparatus using a picture signal based on DV is classified into the 4:2:2 color component type or the 4:4:4 color component type, and the picture signal used in the video apparatus usually is classified into the 4:1:1 color component type.
As compared with MPEG data of an MPEG picture signal based on MPEG1 or MPEG2, when DV data of a DV picture signal based on DV is used, because the DV data are independently used for each frame, an editing operation of the DV data such as "cut & paste" can be easily performed for each frame. Also, because a code volume of the DV data for each frame is high and is almost six times as high as that of the MPEG data, a high quality image can be generally reproduced in case of the DV data.
Also, because the DV data having merits of the high quality image and the easy edition can be input to a computer, when a user operates a computer to process a picture, the user desires to use DV data of the picture in an input operation, an editing operation and a data storing operation for the purpose of easily processing the DV data and reproducing the picture at high quality. Also, the user desires to use MPEG data obtained from the DV data when the user transmits the picture to another computer through an internet or the like.
2.2. Problems to be Solved by the Invention
To produce the MPEG data from the DV data, it is required that the user uses a video apparatus using the DV picture signal as the digital video apparatus 103 and connects the video apparatus with the MPEG encoder 104. Therefore, two apparatuses such as the video apparatus using the DV picture signal and the MPEG encoder 104 are necessarily required, so that the user cannot process a picture at a low cost.
To process the picture at a low cost, there is an idea that the DV data of the picture input to a computer is directly converted into the MPEG data according to a software program without using any MPEG encoder. However, in cases where the DV data is directly converted into the MPEG data according to a software program, there are following problems. That is, there is no method for directly converting a 4:1:1 color component type digital picture signal used in a digital video apparatus, in which the DV data is processed, into a 4:2:0 color component type digital picture signal used for the MPEG data (first problem). Also, in cases where the DV data are decoded and the MPEG data are encoded, because a processing volume of the decoding and encoding operation is large, it takes a lot of time to perform the decoding and encoding operation in a general computer (second problem).